Method of producing a nonwoven fabric from filaments

ABSTRACT

Spun bond is made by collecting thermoplastic filaments on a perforated surface and the spun bond is then subjected to hydrodynamic consolidation with high-pressure water jets. The filaments before the formation of the spun bond or after the formation of the spun bond are treated with a wetting agent prior to the hydrodynamic consolidation.

FIELD OF THE INVENTION

[0001] Our present invention relates to a method of producing a nonwovenfabric, especially a spun-bond web, from filaments and especiallyfilaments of a thermoplastic synthetic resin in which the filaments arehydrodynamically consolidated.

BACKGROUND OF THE INVENTION

[0002] The production of nonwoven fabrics, fleeces and mats fromthermoplastic synthetic resin filaments, hereinafter referred to as websand especially spun-bond webs, is known. The filaments, usually endlessfilaments, i.e. filaments which theoretically can be continuous and arethus distinguishable from so-called staple fibers which are relativelyshort threads, can be collected on a surface and accumulated in a jumbleor random collection of the filaments so as to produce the nonwoven web.The web itself can be fabricated in a continuous manner and the product,when composed of continuous filaments, filaments which are notintentionally broken up or filaments which can be theoreticallycontinuous and thus as long as possible without interruption in theextrusion of the filaments from a spinneret, is known as spun bond.

[0003] The filaments collecting upon a surface tend to bond together atcrossover points. The surface upon which the filaments collect can be amoving surface, preferably the surface of an endless belt whichcirculates below a curtain of the filaments descending from a spinneret.The filaments can be aerodynamically stretched between the spinneret andthe collecting surface.

[0004] The formation of hydrodynamically consolidated spun-bond websfrom filaments or endless strands can be contrasted with the formationof nonwoven webs from shorter fibers in the so-called melt-blownprocess. In the melt-blown process, the strands emerging from thespinneret are broken off to staple fiber and the fiber is collected on asurface. The melt-blown product has a significantly smaller amount oflooping of the strands and fewer runners.

[0005] The spun-bond webs which have been produced heretofore havesomewhat lesser degrees of a fleece characteristic than the melt blownwebs and may have a lesser strength, especially because of a somewhatsmaller degree of consolidation. Further-more, spun-bond webs can show agreater tendency toward abrasion wear than is desirable. Attempts toavoid these drawbacks have led to the development of intensivehydrodynamic consolidation of the web in the case of spun bond which, inturn, leads to greater cost, especially in terms of the cost of energyused in the fabrication process and may contribute to limited productionspeed.

OBJECTS OF THE INVENTION

[0006] It is, therefore, the principal object of the present inventionto provide a method of making spun-bond webs without the drawbacks ofthe earlier systems described.

[0007] More particularly, it is an object of the invention to provide amethod of making hydrodynamically consolidated spun bond at lower costand with higher production speeds than has ben possible heretofore andwhereby there is a more effective binding of the strands and moreintensive interlooping thereof and runner formation therein so that thefleece characteristics of the web are improved and of a satisfactorylevel.

[0008] It is also an object of the invention to eliminate drawbacks ofearlier systems and improve the production rate and quality of a spunbond fleece or web.

SUMMARY OF THE INVENTION

[0009] These objects and others which will become apparent hereinafterare attained, in accordance with the invention, by applying to thefilaments at least one wetting agent and then hydrodynamicallyconsolidating the spun bond which is produced from the filament.

[0010] The method then comprises the steps of producing filaments ofthermoplastic synthetic resin material, treating the filaments which arethus produced with at least one wetting agent and then hydrodynamicallyconsolidating a spun-bond w b formed from these filaments.

[0011] While the filaments can be treated with the wetting agentaccording to the invention before they are collected into the spun bonweb, it is within the scope of the invention to treat the filaments aspart of the spun-bond web. A treatment with the wetting agent, ofcourse, means bringing the filaments or the spun-bond web into contactwith the wetting agent and preferably coating the filaments prior toformation of the web or after formation of the web with the wettingagent.

[0012] In a highly preferred embodiment of the invention, the wettingagent is formed by at least one tenside or surface active agent(surfactant). Such a surfactant has a lipophilic part and a hydrophilicpart or can be a lipophile having hydrophilic ends. The surfactant canespecially be an ionic surfactant, i.e. a cationic or anionicsurfactant, or a mixture of both, or a nonionic surfactant or a mixturethereof with either a cationic or anionic surfactant. Amphotericsurfactants can also be used.

[0013] Following the treatment with the wetting agent, preferably with asurfactant, the spun-bond web or fleece can be hydrodynamicallyconsolidated using water jets. The water jets can be fine jets and/orhigh-speed jets which in effect produce water jet needling of the web,i.e. a partial entrainment of filament loops from one side of the webtoward the opposite side.

[0014] The filaments from thermoplastified synthetic resin can be cooledin a curtain below the spinnerette so that the filaments remain discreteand separate. The filaments can then be stretched, preferablyaerodynamically and collected upon the foraminous or perforated sievebelt which travels continuously past the collecting location, i.e. anendless belt.

[0015] Preferably the application of suction below the belt facilitatesthe deposition of the filaments onto the perforated surface. The suctiondevice can include one or more suction blowers. The resulting spun webis then treated with the wetting agent, preferably surfactant, and thenhydrodynamically consolidated.

[0016] After the collection of the filaments into a spun bond web, thespun-bond web can be precompacted in a calender and, if not treated withthe wetting agent before, can then be treated with the wetting agent.After drying and if desired, a certain ripening or aging period, the webcan be subjected to the water jet needling.

[0017] The method of the invention can also be used to make multilayerproducts or laminates wherein, for example, a spun-bond web treated withat least one wetting agent can be joined to a further layer and theresulting combination of two layers can be subjected to hydrodynamicconsolidation. A further layer of spun bond treated with the wettingagent can be applied and the three-layer composite subjected to thehydrodynamic consolidation.

[0018] The additional fiber layer which is laminated with the spun bondshould be a layer of bibulous or water-absorbent fibers, especiallycellulose fibers. In this case the hydrophilic fibers are sandwichedbetween layers which are treated with the wetting agent or surfactant.

[0019] The application of the wetting agent to the filaments, with orwithout drying and subsequent water jet treatment has been found toproduce spun-bond webs or laminates of surprisingly advantageousproperties. Especially the interlocking of the filaments is greatlyimproved and the filaments are caused to have runners which interlace inan optimal manner to increase the strength of the web by comparison withwebs made at similar cost by earlier techniques. Especially the tensilestrength of the web has been found to be improved by the invention. Theabrasion sensitivity of the web is likewise reduced and the energy costswith the hydrodynamic consolidation are significantly lower than forearlier methods. At the same time the production speed can be increased.

[0020] As a general matter, with the method of the invention, combiningthe application of the wetting agent with the needling of the web withwater jets, the mechanical properties of the spun bond web or fleece aresignificantly improved by comparison with spun bond fabricated withoutthe hydrodynamic consolidation on the one hand and with spun bond whichmay be treated with the wetting agent on the other. These advantages areclearly unexpected based upon the knowledge in the art.

BRIEF DESCRIPTION OF THE DRAWING

[0021] The above and other objects, features, and advantages will becomemore readily apparent from the following description, reference beingmade to the accompanying drawing in which:

[0022]FIG. 1 is a diagrammatic illustration of the method of theinvention; and

[0023]FIG. 2 is a more detailed diagram illustrating features of theinvention.

SPECIFIC DESCRIPTION

[0024] The apparatus illustrated diagrammatically in FIG. 1 andrepresenting part of a system for producing spun bond web according tothe invention includes a perforated belt 2 upon which the filaments 1are deposited to form the spun bond web. The belt 2 moves continuouslypast the filament deposition site as represented by the arrow A andcarries the spun bond into a first treating station 4 in which thewetting agent is applied and then into a water jet needling station 5 inwhich high pressure water jets are trained on the web to consolidate theweb hydrodynamically.

[0025] From FIG. 2 it will be apparent that the filaments 1 can beproduced from molten thermoplastic synthetic resin, supplied by athermoplastifier as represented at 6 by a conventional spinnerette 7.The filaments 1 may be cooled by cooling air supplied at 8 in a coolingzone 9 and then aerodynamically stretched in a zone 10 by passingthrough a Venturi-like passage 11. Below the perforated belt 2, asuction blower 12 can provide suction to draw the filaments onto thebelt. The belt is an endless belt which is continuously moving.

[0026] In the system shown in FIG. 1, the spun-bond web 3 can initiallypass between a pair of calendering rollers 13 and can then be treatedwith the wetting agent by a spray head 14. Optionally the spun-bond web3 can be dried, for example under a drying hood with warm air suppliedby a blower 16. In the hydrodynamic consolidation zone 17, high pressurewater is directed from needle jets 18 against and onto the spun-bondweb.

[0027] If desired, a layer 19 of cellulose fibers may be dispensed ontothe surface of the spun-bond web 3 by a dispenser 20 and the combinationof the cellulose fibers and spun-bond layer supporting same may beneedled with high-pressure water jets at 21.

[0028] The needling at 21 may be the first needling to which thecomposite is subjected if needling at 17 of the spun bond is omitted. Afurther layer 22 of spun bond treated with the wetting agent may then beapplied at 23 and the composite or laminate 24 may be subjected tohydrodynamic consolidation with high-pressure water jets from nozzles25. The resulting product can be dried. The spun bond 3 has increasedstrength and reduced tendency to abrasion and the composite, if formed,has in addition the highly bibulous properties contributed by thecellulose fiber.

We claim:
 1. A method of making a spun-bond web comprising the steps of:(a) forming filaments of thermoplastic synthetic resin; (b) collectingsaid filaments in a spun-bond web; (c) treating said filaments with awetting agent; and (d) hydrodynamically consolidating said spun-bondweb.
 2. The method defined in claim 1 wherein said filaments areproduced with a spinnerette and are then cooled.
 3. The method definedin claim 2 wherein said filaments are collected on a continuously movedforaminous belt.
 4. The method defined in claim 3, further comprisingdrawing air through said belt from below said belt in a region at whichsaid filaments are collected on said belt with at least one suctiondevice.
 5. The method defined in claim 4 wherein said filaments aretreated with said wetting agent after the filaments have been collectedinto a spun-bond web on said belt.
 6. The method defined in claim 5wherein said wetting agent is a surfactant.
 7. The method defined inclaim 6 wherein said spun-bond web is hydrodynamically consolidated bytraining water jets thereon.